Optical lithography tools use a single light source (e.g., a laser) to align and expose a lithography mask on a semiconductor wafer. In a typical semiconductor wafer process that uses photolithography, alignment marks do not generate a high backscattered electron contrast when probed with the electron beam in an electron beam lithography exposure tool. Therefore, detection of typical photolithography alignment marks using an electron beam with SCALPEL (Scattering with Angular Limitation In Projection Electron-Beam Lithography) is not possible. Only after alignment marks are defined on or in the wafer, that can be detected with electrons, can a SCALPEL tool be used to expose the mask features on the wafer. Thus the SCALPEL tool uses an electron beam source to align the lithography mask, and an electron beam source to expose the mask on the wafer.
There, thus, exists a need in the art for a method and structure that permits the use of an electron-beam source for both alignment and exposure of a lithography mask on a semiconductor wafer.